Evaluation of the Oxygen Gas Coverage in the Anodic Flow Field and Its Impact on the Performance of a PEM Electrolysis Cell

Proton exchange membrane (PEM) electrolysis provides promising opportunities to produce green hydrogen and thus for upscaling the storage of renewable energy. [1] The aim of future developments of the PEM electrolyzers is to increase the performance by increasing the cell areas and applying higher current densities. In this case the two-phase flow plays a significant role as a large amount of gas is produced and poor removal has a negative impact on the electrochemical process. To ensure effective mass transport, the dynamics of bubble formation and the phenomena of two-phase flow must be thoroughly investigated. [2] In previous studies transparent cells were operated to analyze the bubble formation micro- and macroscopic using high-speed video recordings in at various flow rate, temperatures and current densities. [3,4] To establish a connection between electrochemical measurements such as polarization curves and EIS measurements and the video data, a transparent proton exchange electrolysis cell (PEMEC) with an active area of 25 cm 2 was operated up to a current density of 3.5 A·cm -2 . In 0.1 A·cm -2 steps EIS measurements and video recordings of the anode-side two-phase flow were conducted while the polarization curve was performed. To observe the effects from low water supply a low flow rate of 3 ml/min was chosen so that a low stoichiometric ratio λ = 6 - 8 is present at high current densities. The video data was quantitatively evaluated by a novel algorithm based on artificial intelligence (AI) and correlated with the polarization curve and EIS measurements. Individual gas bubbles could be distinguished up to current densities of 2.6 A·cm -2 by the algorithm, which indicated enhanced gas coverage and bubble size with increasing current density. Calculations based on a two-phase flow mixture model revealed a similar trend in the local distributions of gas content within the flow field. Reaching higher current densities, the transition of the flow regime from two-phase flow with individual gas bubbles to an interconnected gas flow regime in large part of the cell was observed along with a strongly increasing voltage and changes in the impedance pattern. Thus, the results demonstrate the importance of analyzing the gas coverage and flow for the evaluation of the performance of PEM electrolyzers. Literature [1] M. Carmo et al. , Int. J. Hydrogen Energy 2013, 38, 4901. [2] S. Yuan et al. , Progress Energy Combustion Sci. 2023, 96, 101075. [3] J.C. Garcia-Navarro et al. , Int. J. Hydrogen Energy 2019, 50, 27190. [4] J.O. Majasan et al. , Int. J. Hydrogen Energy 2018, 43, 15659. *This work was financially supported by the BMBF: Wasserstoff - Leitprojekt H2Giga, Teilvorhaben DERIEL (project number 03HY122C).